GeoJSON plugin has no option to read Feature.id from source

[montzkie18]

Related to this issue: mapnik/node-mapnik#707

I have a use case where I create VectorTiles from a GeoJSON source, using node-mapnik.
Unfortunately mapnik's geojson datasource ignores Feature.id by design to assign an incremental id instead.

It would be great to have a flag to force the GeoJSON plugin to read the ids from the source instead, giving users the responsibility of making those ids unique.

The flag makes it opt in and disabled by default to maintain the current behavior.

[YousefED]

Agree this would be useful!